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Summary Table

Feature	Detail
Risk Factors	Trauma to the medial aspect of the eyelid or midface; dog bites to the face (especially in children); assault, motor vehicle accidents, falls against sharp objects
Etiology	Direct traumatic disruption of the lacrimal drainage apparatus (canaliculus, lacrimal sac, or nasolacrimal duct)
Patient Presentation	Laceration of the medial eyelid or medial canthal region, often with persistent tearing (epiphora) from the affected eye
Classic Physical Exam	Eyelid laceration medial to the lower punctum, visible fat prolapse (suggesting orbital septum violation), flattened or disrupted medial canthal angle, epiphora
Key Diagnostic Results	Clinical identification of laceration location relative to the punctum; probing and irrigation of the canalicular system; CT of the orbits/midface if bony injury is suspected
Management	Canalicular repair over a silicone stent by an ophthalmologist or oculoplastic surgeon within 48 hours; primary microsurgical anastomosis of the severed canaliculus
Keywords	"Laceration medial to the punctum," "persistent tearing after eyelid repair," "dog bite to medial canthus," "silicone stent intubation"

1. Pathophysiology

The lacrimal drainage system begins at the puncta, small openings located on the medial aspect of both the upper and lower eyelid margins. Tears drain through the puncta into the superior and inferior canaliculi, which converge at the common canaliculus before emptying into the lacrimal sac, seated within the lacrimal fossa of the medial orbital wall. From there, tears flow through the nasolacrimal duct and exit beneath the inferior turbinate in the nasal cavity.

When a laceration occurs medial to the punctum on either eyelid, the canaliculus is at direct risk of transection. The inferior canaliculus is the primary drainage conduit, handling roughly 70% of tear outflow, which is why injuries to the lower lid medial to the punctum carry the greatest functional consequence. If the severed canaliculus is not identified and repaired, the cut ends will scar and fibrose, creating a permanent obstruction. The patient then develops chronic epiphora (overflow tearing) because tears can no longer reach the lacrimal sac and drain into the nose.

The reason dog bites are so frequently tested is anatomical: a dog's canine teeth tend to grasp and tear the medial canthal region of the face, and in children, the bite height aligns perfectly with the medial eyelid. This mechanism produces irregular, crushing wounds that often transect the canaliculus while also introducing infection risk from oral flora.

A laceration lateral to the punctum, by contrast, does not involve the drainage apparatus and can be closed primarily without concern for epiphora. This anatomical landmark is the single most important distinction the exam tests.

2. Classification and Clinical Manifestation

Classification	Anatomic Level	Clinical Implication
Canalicular laceration	Punctum through common canaliculus	Most commonly tested; requires stented microsurgical repair to preserve tear drainage
Lacrimal sac laceration	Lacrimal fossa (medial canthal tendon area)	Often associated with medial canthal tendon avulsion and naso-orbito-ethmoid fractures; may need dacryocystorhinostomy
Nasolacrimal duct injury	Within the bony nasolacrimal canal	Typically secondary to midface (Le Fort II/III) or naso-orbito-ethmoid fractures; addressed during fracture repair

Canaliculus Involved

Involved Canaliculus	Functional Impact
Inferior canaliculus only	High impact; carries the majority of tear drainage; repair is essential
Superior canaliculus only	Lower functional impact; repair still recommended but isolated injury may be tolerated
Both canaliculi (bicanalicular)	Severe; guarantees epiphora if not repaired

3. Diagnostic Workup

Test	Role	Findings
Clinical inspection of wound location	Best initial assessment	Laceration medial to the punctum on upper or lower lid strongly suggests canalicular involvement
Canalicular probing and irrigation	Confirmatory test	A probe or irrigating cannula is passed through the punctum; failure to pass the probe through the full length of the canaliculus, or irrigation fluid exiting through the wound rather than draining into the nose, confirms transection
CT orbits and midface	Adjunctive if bony injury suspected	Evaluates for naso-orbito-ethmoid fractures, orbital floor fractures, or lacrimal sac/duct-level bony disruption
Dye disappearance test	Functional assessment (post-repair or chronic cases)	Fluorescein instilled in the conjunctival fornix; delayed or absent clearance indicates drainage obstruction

The workup begins at the bedside. Any eyelid laceration must be evaluated for its position relative to the punctum. If the wound is medial to the punctum, canalicular injury should be assumed until proven otherwise. A common pitfall is closing a medial eyelid laceration in the emergency department without first assessing the canalicular system, because the external wound may look deceptively simple.

Formal probing and irrigation is performed under magnification, ideally by an ophthalmologist. A lacrimal probe or small-gauge cannula is inserted through the intact punctum into the canaliculus. If the probe exits through the wound or saline irrigated through the punctum leaks from the laceration rather than reaching the nose, the canaliculus is confirmed to be transected.

CT imaging is not required for an isolated soft-tissue canalicular laceration but becomes necessary when the mechanism suggests midface fractures, such as high-energy blunt trauma or motor vehicle collisions. Naso-orbito-ethmoid fractures can disrupt the lacrimal sac or nasolacrimal duct at the bony level.

4. Management and Treatment

Step	Intervention	Details
Acute stabilization	Wound care and tetanus prophylaxis	Irrigate the wound; do not close the medial lid laceration primarily if canalicular injury is suspected; cover with moist dressing
Antibiotics (if bite wound)	Amoxicillin-clavulanate 875/125 mg PO twice daily for 5 to 7 days	Covers Pasteurella, streptococci, anaerobes from dog/cat bite flora
Definitive repair	Canalicular repair over a silicone (Crawford) stent	Microsurgical anastomosis of the cut canalicular ends; silicone tubing is threaded through both canaliculi, into the lacrimal sac, and out through the nasolacrimal duct into the nose, where it is tied off
Timing	Within 48 hours of injury	Delayed repair beyond 48 hours leads to tissue retraction and fibrosis, making anastomosis technically difficult and outcomes poorer
Stent removal	3 to 6 months post-repair	Stent is left in place to maintain patency during healing; premature removal risks re-stenosis
Late presentation or failed repair	Dacryocystorhinostomy (DCR)	Creates a new drainage pathway directly from the lacrimal sac into the nasal cavity, bypassing the obstructed canalicular system

The cardinal rule in the emergency setting is: do not close a medial eyelid laceration without first ruling out canalicular involvement. If the wound is medial to the punctum, the patient should be referred to ophthalmology or oculoplastic surgery for definitive repair rather than having the wound closed primarily by the emergency physician.

The repair itself involves identifying both cut ends of the canaliculus under an operating microscope. The distal (lacrimal sac) end can be located by irrigating through the opposite intact canaliculus and watching for fluid egress in the wound. A silicone stent is passed through the system to act as an internal scaffold, and the canalicular mucosa is reapproximated with fine absorbable sutures (typically 7-0 or 8-0 polyglactin). The overlying lid tissue is then closed in layers.

For dog bite wounds, antibiotic prophylaxis with amoxicillin-clavulanate is standard. Rabies post-exposure prophylaxis should be considered based on the animal's vaccination status and local epidemiology.

If the injury presents late (weeks to months later) with established scarring and chronic epiphora, primary repair is no longer feasible. The standard salvage procedure is a dacryocystorhinostomy, which bypasses the canalicular obstruction entirely.

5. Differential Diagnosis and Distractors

Differential Diagnosis	Why It Looks Similar	Key Discriminator
Simple eyelid laceration (lateral to punctum)	Also a traumatic lid wound, may also have tearing from irritation	Wound is lateral to the punctum; canalicular system is intact; probing and irrigation are normal; can be closed primarily
Orbital septum violation with fat prolapse	Medial eyelid trauma with visible fat in the wound	Fat prolapse indicates a full-thickness lid laceration through the septum, but this can occur with or without canalicular injury; the key is still whether the wound is medial to the punctum
Medial canthal tendon avulsion	Medial canthal trauma with telecanthus (widened intercanthal distance)	The tendon inserts on the anterior and posterior lacrimal crests; avulsion causes rounding and lateral displacement of the medial canthus, often with an associated naso-orbito-ethmoid fracture; canalicular injury may coexist but tendon repair is the primary concern
Dacryocystitis	Presents with tearing and medial canthal swelling	Dacryocystitis is an infectious process of the lacrimal sac; there is no trauma history; the hallmark is a tender, erythematous swelling below the medial canthal tendon with expressible purulent material from the punctum
Nasolacrimal duct obstruction (congenital)	Presents with chronic epiphora	Seen in infants, not associated with trauma; caused by a persistent membrane at the valve of Hasner; treated initially with lacrimal sac massage, not surgical repair

6. Traps and High-Yield Pearls

The most common way students lose points on this topic is by failing to recognize that a medial eyelid laceration is not just a wound to close but a potential canalicular injury requiring subspecialty repair. The vignette will describe a patient with a laceration "near the inner corner of the eye" or "medial to the punctum," and the wrong answer will be primary wound closure in the emergency department. The correct answer is ophthalmology consultation for canalicular exploration and stented repair.

A second frequently tested trap involves the mechanism. When a child presents after a dog bite to the face with a wound near the medial canthus, students may focus on wound infection management and miss the canalicular injury. The exam expects you to recognize that the anatomic location of the wound, not just the etiology, determines the next step. Antibiotics address the bite, but the wound itself needs operative canalicular repair.

Finally, remember the timing window. Canalicular repair should be performed within 48 hours. A vignette describing a patient who presents days to weeks after injury with persistent tearing is testing whether you know that primary repair is no longer viable and that the answer has shifted to dacryocystorhinostomy.

The core competency being tested is anatomical reasoning: can you use the location of a wound relative to the punctum to predict which deeper structures are at risk and, from that, determine the correct management pathway?

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